Process for the stabilizing of an organosilane

ABSTRACT

A process for the stabilizing of an organosilane with an effective, stabilizing amount of purified N,N&#39;-diphenyl-p-phenylenediamine (DPPD). The purification of crude DPPD involves extracting crude DPPD with hexane thereby forming an extract solution containing DPPD, passing the extract solution over an adsorption layer comprising silica gel as the adsorbent to form a solution containing purified DPPD and recovering the purified DPPD from the solution.

This application is a Divisional of application Ser. No. 08/777,702,filed on Dec. 20, 1996, now U.S. Pat. No. 5,763,666.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process and to an apparatus for thepurification of crude diphenyl-p-phenylenediamine (DPPD) and to the useof purified DPPD.

2. DESCRIPTION OF THE BACKGROUND

DPPD is used on a large industrial scale as a stabilizer, inter alia, inthe reaction of potassium methacrylate with3-chloropropyltrimethoxysilane. In this application, the use ofcommercially available DPPD can impair product quality, in particularthe color number of the product. Unfortunately, in the past, industrialquantities of DPPD have only been available on the market in a technicalquality.

Crude DPPD, that is, commercially available DPPD or technically pureDPPD has, as a rule, a purity in the range around 85% by weight, theremainder of about 15% by weight essentially consisting of unconvertedor incompletely converted starting materials such as, for example,diphenylamine, and of inorganic components such as iron and chlorine,for example in the form of iron chloride. The commercial material isgray and is often in the form of a powder or in the form of flakes. Incontrast thereto, pure DPPD is white and crystalline.

Several methods for the purification of DPPD are described in theliterature. It is possible to crystallize DPPD from chlorinatedhydrocarbons or carbon tetrachloride (Beilstein E III 13, 4^(th) Auflage1973, pages 115-118, The Merck Index 9^(th) Edition 1976, page 445). Thedisadvantage of these processes is, however, the use of chlorinatedsolvents which are toxic and pollute the environment.

Another purification method is solids distillation. This method can beapplied successfully in the laboratory. For the purification of crudeDPPD on an industrial scale, however, solids distillation is not asuitable process, since it is too expensive in engineering terms. A needtherefore continues to exist for a method of inexpensively andeffectively purifying DPPD.

SUMMARY OF THE INVENTION

Accordingly, one object of the present invention is to provide a processwhich allows crude DPPD to be purified in a simple and economicalmanner, thereby making a purified DPPD product available for applicationon an industrial scale.

Briefly, this object and other objects of the present invention ashereinafter will become more readily apparent can be attained in aprocess for purifying crude N,N'-diphenyl-p-phenylenediamine (DPPD),comprising extracting crude DPPD with a hydrocarbon or hydrocarbonmixture, passing the extract over an adsorption layer and recoveringpurified DPPD from this solution. Preferably, the purification iscarried out under a blanketing gas.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a flow diagram showing apparatus components of a preferredembodiment of the invention for purifying DPPD; and

FIG. 2 is a flow diagram of a preferred embodiment of the apparatusarrangement of the extraction unit of the flow process shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Surprisingly, it has now been found that, by extracting crude DPPD witha hydrocarbon or a mixture of hydrocarbons and passing the extract overan adsorption layer, pure DPPD, preferably white and in crystallineform, is obtained in a simple and economical manner from the solutionwhich has been prepared. In the present process, industrial DPPD canalso be used as the crude DPPD.

FIG. 1 shows the flow diagram of a preferred embodiment of the equipmentin which the process of the invention can be carried out.

The apparatus for the purification of N,N'-diphenyl-p-phenylenediamine(DPPD) comprises a solvent evaporator (1) to which is attached adownstream condenser (3) which is connected via a solvent line (5) to anextraction unit (7) which in turn is equipped with an interior andliquid-permeable container (8) in which DPPD is extracted from crudeDPPD (9) and with a downstream adsorption layer (11). Layer (11) isconnected via an extract line (13) to the solvent evaporator (1) whichin turn is coupled at the bottom via a lock (15) to a filter unit (17).A filtrate line (19) leads via a pump (21) to the solvent evaporator(1). Suitably, one or more blanketing gas line(s) (23) and/or (25) arealso provided in the apparatus.

The apparatus embodiment, shown in FIG. 2, is a preferred embodiment ofthe extraction unit and employs extraction vessel (41) in which DPPD isextracted from crude DPPD (9) and a vessel (43) which is connectedthereto via a line system (45) and which contains an adsorbent layer 44.Suitably, the extraction unit is equipped with a crude product feeder(47) and/or a residue outlet (49). Furthermore, however, the solventevaporator (1), the extraction unit (7) and the filtration unit (17) canalso be equipped with a material feeder lock or a material removal lock.

In order to achieve more thorough mixing in the relevant solid/liquidphases or also better heat transfer in the liquid phases, the apparatusof the invention can also be equipped, with respect to units (9), (41)and (1), with a stirrer or mixer unit.

For the recovery of purified DPPD, the present apparatus can also beequipped, in place of filtration unit (17), with other separationdevices, known per se for the separation of solid/liquid systems, suchas a centrifuge or a decanter.

In general, the process of the invention is carried out as follows:

Hydrocarbons or hydrocarbon mixtures can initially be introduced intothe solvent evaporator (1). The quantity of extractant introduced heredepends as a rule on the size of the apparatus or unit available.

In general, all cyclic, aliphatic or aromatic, but also acyclic branchedor unbranched hydrocarbons having 3 to 10 carbon atoms are suitable asextracting solvents. For carrying out the extraction, preferablypentane, cyclopentane, hexane, cyclohexane, benzene, toluene, heptane,cycloheptane and many others are used. In the process of the invention,the extraction is carried out with particular preference for hexane,which includes all of its isomers and isomer mixtures. However,unsaturated cyclic or acyclic hydrocarbons such as cyclopentene,pentene, cyclohexene, cyclohexadiene, hexene and many others, can alsobe used as extractants in the process. Likewise, mixtures ofaliphatically saturated, aliphatically unsaturated, cyclic, acyclic andaromatic hydrocarbons can also be used.

As a rule, the solvent evaporator (1) is operated under normal pressureat a temperature in the range from 40 to 110° C. The solvent fractionthus transferred into the gas phase is suitably passed through acondenser (3) and the condensate which forms is fed via a solvent lineto the extraction vessel (7).

The extraction containers (8) and (41), which are permeable to liquids,of the extraction unit can consist of a textile fabric which can be madeof a polyester, polyamide or another polymer, and/or can consist of ametal fabric. The mesh width of such fabrics is usually in the rangefrom 0.01 to 0.2 mm. The extraction vessel, which is permeable toliquids, and/or the bottom for taking up an adsorbent can, however, alsoconsist of ceramic materials, for example of G 1-G 4 fritted glass.

The part of each absorption layer (11) and (44), which is suitablyequipped with a liquid-permeable bottom, can be covered by a layer ofadsorbent. The adsorbent used in the process of the invention ispreferably silica gel, for example a silica gel made by MERCK. For suchadsorption layers, layer thicknesses in the range of from 2 cm to 30 cmare preferred, but the layers can also be thicker. Thus, for example asilica gel having a mean grain size of from 0.063 to 3.00 mm can be usedhere, and the silica gel preferably used has a mean grain size from0.063 to 0.5 mm. A particularly preferred silica gel is a silica gelhaving a mean grain size from 0.20 mm to 0.5 mm. In particular a silicagel having a BET surface area of from 450 to 550 m² /g. Aliquid-permeable extraction vessel (8) filled with commerciallyavailable DPPD can be located above the adsorption layer (11). Theextraction unit (7) prepared in this way is in general sealed gas-tightand charged via the condensate line (5) with solvent.

The extraction vessel (8) and the vessel for the adsorbent layer (11)can of course also be arranged separate from one another, in which casethe crude extract can be fed from the extraction vessel (41) via a line(45) to the adsorbent vessel (43) which contains adsorbent layer 44. Apreferred embodiment for this purpose is shown in FIG. 2.

Suitably, the crude DPPD first introduced into the extraction vessel (8)or also into unit (41) is covered with extractant. However, theextraction vessels (8) and (41) as a rule are filled up to a level whichcorresponds to the highest point in the extract discharge (13) or (45).When this level is reached, the extract flows off because of thesiphoning effect into the solvent evaporator (1) or via the vessel (43)into the solvent evaporator (1).

In the process of the invention, the extraction is generally carried outat a temperature in the range of from 40 to 100° C. The adsorption is asa rule also carried out at a temperature in the of range from 40 to 100°C.

In a suitable manner, the adsorption layers (11) and (44) then take upparticles present in the extract and impurities which cause turbidity,so that the solution flowing off into the solvent evaporator (1) isclear. The process of the invention can be carried out under normalpressure, at reduced pressure or even at slightly elevated pressure.

It has been found that it can be expedient to insulate the extractionunit (7), as well as units (41) and (43), including the lines (45), aswell as (13) and (15) against heat losses. It is also possible toprovide trace-heating for the extraction unit (7), as well as units (41)and (43) including the lines (45), as well as units (13) and (15).

Crude DPPD (9) can be charged to the extraction vessels (8) and (41)discontinuously or continuously. Especially for carrying out the processof the invention continuously, the extraction vessels (8) and (41) canbe equipped with a product-charging device for crude DPPD, for example,(47), and a discharge device for the extraction residue, for example,(49). The adsorbent vessels, for example, (43) can also be equipped withsuitable locks for the removal of spent silica gel and for the chargingof fresh silica gel. Such an arrangement is advantageous for increasingthe plant capacity for the production of purified DPPD.

The equipment of the invention is advantageously blanketed with inertgas, for example nitrogen (23) and (25), in order to prevent theformation of ignitable mixtures.

After several extraction cycles, the purification of DPPD can beobserved by how it crystallizes as a white microcrystalline powder fromthe supersaturated solution in the solvent evaporator (1).

The process of the invention for the purification of crude DPPD can becarried out discontinuously or continuously. In discontinuous operationof the unit, the extraction vessel (8) or (41) is suitably emptied andrefilled with crude DPPD several times before the extraction is stoppedand the purified product is isolated from the extractant. In this case,2 or 3 emptying and filling steps are preferred before the pure DPPD isisolated. The adsorption layer (11) or (44) can be partially orcompletely replaced. It is, however, also possible to run severalextractions through the same adsorption layer, without impuritiespassing into the solvent evaporator (1). The extraction period is as arule 20 to 60 hours, so that in general the mean residence time of theproduct in the purification process is also 20 to 60 hours. Experienceshows that an extraction period of about 35 hours is to be preferredfrom the viewpoint of space/time yields. In the process of theinvention, yields of 60 to 85%, relative to the crude DPPD employed, aregenerally achieved, which is to say that the process of the inventioncan also be operated without a loss of valuable product.

After termination of the extraction, the suspension consisting ofextractant and purified crystalline DPPD is, for example, drained onto afilter (17) and separated. The filtrate is clear and can in general beused for further extractions, even without further purification (compare19 and 21). However, the filtrate can also first be distilled beforere-use.

The purified DPPD present can, for example, be dried in vacuo orisolated, under a stream of nitrogen, as a white to light-beigemicrocrystalline powder. The product purified by the process of theinvention has in general a purity of >90%, preferably >95% and veryparticularly preferably 97 to 99% (determination by NMR spectroscopy).The DPPD purified by the invention preferably has a melting range in thetemperature range of from 142° C. to 154° C., and purified DPPD having amelting range in the temperature range of from 144° C. to 148° C. isparticularly preferred. In contrast thereto, the commercially availablecrude DPPD, having a purity of about 85%, has a melting range of from124 to 126° C.

When DPPD purified by the process of the invention is employed, forexample, for the stabilization of MEMO(3-methacryloxypropyltrimethoxysilane) (compare German PatentSpecification 3,832,621), the product thus obtained is distinguished bya particularly outstanding color number.

Another aspect of the invention is the use of DPPD, purified by theprocess of the invention, for the stabilization of organosilanes,containing methacryloxy or acryloxy groups, of the formula I ##STR1##wherein R is a hydrogen atom or a methyl group, R¹ and R² are identicalor different alkyl groups having 1 to 4 C atoms or phenyl groups and mis equal to 0, 1 or 2.

The purified DPPD of the invention can also be used in tire manufacture.

A further advantage of the process of the invention is that, because ofthe use of largely non-polluting hydrocarbons, methods using chlorinatedhydrocarbons as extractants do not have to be employed.

Having generally described this invention, a further understanding canbe obtained by reference to certain specific examples which are providedherein for purposes of illustration only and are not intended to belimiting unless otherwise specified.

EXAMPLE 1

An extraction vessel, fitted with a liquid-permeable bottom, is filledwith 5.5 kg of silica gel 60 (grain size 0.2 to 0.5 mm) made by MERCK,which is mixed with 4 kg of ceramic saddle-type packing having adiameter of 15 mm. Above this adsorption layer, a liquid-permeableextraction vessel containing 10 kg of crude DPPD made by GOBEL andPFRENGLE is suspended from the lid of the extraction vessel.

300 l of hexane (an isomer mixture having a boiling point of 68° C.),manufactured by OLFABRIK Lahr, is first introduced into the solventevaporator. The unit is permanently blanketed with dry nitrogen, so thatatmospheric oxygen and atmospheric humidity can be excluded.

The extractant is heated to the boil. A temperature of 68° C. ismeasured at the base of the extraction unit. The condensate flows viathe condensate line into the extraction vessel and from there, dependingon the filling level in the extraction vessel, with dissolved DPPD backinto the solvent evaporator. The extraction cycles are repeated over aperiod of 60 hours. The extraction unit is then opened to remove theextraction vessel. The residue is removed from the extraction vessel.Weighing after drying gives a quantity of 1.5 kg of residue. The silicagel is replaced by 6 kg of fresh silica gel containing 4 kg ofsaddle-type packing. The extraction vessel filled with 10 kg of crudeDPPD is reinserted into the extraction vessel. After an extractionperiod of 36 hours, 1.5 kg of residue are obtained.

The content from the solvent evaporator is drained onto a filter. Thefilter cake is washed twice with about 18 kg of hexane and dried invacuo with a little nitrogen being introduced simultaneously. Thisprocedure provides 16 kg of pure DPPD as a light-beige microcrystallinepowder. This corresponds to a yield of 80%, relative to the totalquantity of crude DPPD employed.

EXAMPLE 2

Quantities employed for one extraction:

i) 4 kg of silica gel 60 (0.2 to 0.5 mm)=55 mm layer height,

ii) 1.5 kg of used silica gel (yellow)=25 mm layer height,

iii) 4 kg of saddle-type packing: Total height of the adsorptionlayer=80 mm,

iv) 400 l of hexane (isomer mixture),

v) 9 kg of crude DPPD (flakes).

After an extraction period of 40.5 hours, the amount of residue was 2.5kg and the amount of extracted DPPD was 6.5 kg.

EXAMPLE 3

Quantities employed for the first extraction:

i) 4 kg of silica gel,

ii) 1.5 kg of used silica gel,

iii) 9 kg of crude DPPD (powder),

iv) 400 l of hexane.

Quantities employed for the second extraction:

i) 3 kg of unused silica gel 60,

ii) 3 kg of used silica gel 60,

iii) 4 kg of saddle-type packing

iv) 10 kg of crude DPPD (flakes)

From 19 kg of crude DPPD, 12.5 kg=67% of pure DPPD were isolated in theform of a white powder.

Having now fully described the invention, it will be apparent to one ofordinary skill in the art that many changes and modifications can bemade thereto without departing from the spirit or scope of the inventionas set forth herein.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:
 1. A method of stabilizing an organosilane,comprising: ##STR2## extracting crude N,N'-diphenyl-p-phenylenediamine(DPPD) with hexane thereby forming an first extract solution containingDPPD;passing the extract solution over an adsorption layer comprisingsilica gel as the adsorbent to form a second solution containingpurified DPPD; recovering said purified DPPD from the second solution;and blending an effective, stabilizing amount of said recovered,purified DPPD with an organosilane containing methacryloxy or acryloxygroups, of the formula: ##STR3## wherein R is a hydrogen atom or amethyl group, R¹ and R² are identical or different alkyl groups having 1to 4 carbon atoms or phenyl groups, and m is equal to 0, 1 or 2.